More stringent fuel economy regulations in the transportation industry have prompted the need for improved efficiency of the IC engine. Light-weighting, friction reduction, thermal management, variable valve timing, and a diverse array of variable valve lift technologies are all part of the technology toolbox for IC engine designers.
VVL systems of IC engines often manage hydraulic fluid flow, leakage or pressure within a network of fluid galleries to vary the output of these systems. An example of this type of VVL system can be found in U.S. Pat. No. 5,839,400. Precise control of these hydraulic systems is required to achieve optimum engine performance, and maintaining this performance over several years and miles is critical to meeting customer demands.
Noise, vibration and harshness (NVH) demands are becoming more and more stringent for today's automobiles. Cabin noise levels continue to decrease with the aid of noise-cancelling technology, active and passive vibration control components, glass technologies and efforts to reduce IC engine noise. IC engine noise sources can include combustion, mechanical, or fluid-induced noises. Fluid-induced noises can include air flow (intake and exhaust) and hydraulic fluid flow noises. For hydraulically controlled VVL systems, fluid flow noises can be audible, especially when large pressure differentials exist within the fluid gallery network. Such large pressure differentials can be present in cold conditions when hydraulic fluid pressure is high and filling of galleries or chambers is necessary for valve actuation. To alleviate such fluid flow noises, hardware and/or fluid gallery modifications can be implemented, however, such solutions can be costly and require valuable development time. A low-cost resolution is required that minimizes integration effort within a VVL system.